You can change the “Show order summary” link text on mobile. Many merchants do this to help their customers find the coupon code section on the mobile version.
To change this, go to CheckoutWC > Pages > Checkout and open the Mobile Options section. Enter your wording in the Cart Summary Mobile Label field and save.

If you are already working in the Checkout Editor, the same field is available in its checkout settings panel, so you do not need to leave the editor to change it.
Here is how it looks on the front end:

Leave the field blank to keep the default text, Show order summary.
For the feature itself and its other options, see Mobile Cart Summary and Cart Summary.
Another method
The previous way to handle this was using a filter. This still works if for some reason you don’t want to control this from settings.
Note that the filter only runs when the Cart Summary Mobile Label field is empty. A value in that field always takes priority over the filter.